"In place" foaming is a process in which two reactive components are brought together in a mixing head where they react. The resulting reaction mixture is then transferred to a mold where the mixture is foamed and cured into a solid resin. While this process is known for foams comprised of reactive systems such as polyurethane and polyisocyanurate resins, it has not hitherto been practical to apply it to foams comprised of phenol-formaldehyde resins.
A mixing head for use in carrying out "in place foaming" is described in Fiorentini, U.S. Pat. No. 4,332,335. The head comprises a mixing chamber which communicates with a discharge orifice and first and second ducts which dispense the reactive components into the mixing chamber. Means are provided for regulating the flow of the reactants to the reaction chamber.
Phenol-formaldehyde resins can be produced from partially-reacted phenol-formaldehyde resins known as "resols". Resols are resins which are made by reacting a phenol, normally phenol itself, with formaldehyde, using an excess of formaldehyde. The resulting low polymer or oligomer has reactive methylol groups which can react further to enlarge and cross-link the polymer into a cured, three-dimensional network. If the curing is carried out in the presence of a blowing agent, the product is a phenolformaldehyde foam. It is known to use, e.g., chlorofluorocarbons as blowing agents.
Typically, phenol and formaldehyde are reacted in the presence of a basic catalyst such as sodium hydroxide and triethyl amine, followed by neutralization and distilling off water. The initially produced resin is called an A-stage resin. It is known to add urea to this initial product. The A-stage resin can then be reacted further in the presence of an acid catalyst, during which time some formaldehyde and water are liberated. If urea is present, the formaldehyde, may react with the urea to form bis methylol urea, which can also polymerize.
Typical phenolic resin foams are rigid. To increase the flexibility of these foams, large quantities of elastomers are admixed therein. However, the foam then has the qualities of the elastomers, such as low temperature resistance and emission of toxic fumes when burned. There is a great need for a flexible phenolic resin foam which does not require the use of elastomers.